Foliar gas-exchange characteristics of four aquatic macrophytes.
Garnet, Kristy*,1, Taylor, George 1, 1 George Mason University, Fairfax, VA
ABSTRACT- Measurements of the instantaneous gas exchange of carbon dioxide and water as a function of irradiance and carbon dioxide concentration were made in a whole-plant, open gas exchange system that allowed for precise control of the environment (i.e., irradiance, carbon dioxide concentration, temperature). The objective was to compare the characteristics of net photosynthesis among four ecologically distinct emergent macrophytes (i.e., Juncus effusus L., Peltandra virginica L., Orontium aquaticum L., and Taxodium distichum L.). All measurements were normalized to projected leaf area. From the asymptotic responses of net photosynthesis as a function of irradiance (0 - 1200 mol m-2 s-1), statistically significant differences (p ≤ 0.001) among the four species were observed for maximum net photosynthesis (2.7 to 12.6 mol CO2 m-2 s-1) and quantum efficiency (0.036 to 0.142 mol CO2 mol PPFD-1). Equally pronounced differences among species in maximum net photosynthesis (10.0 to 23.3 mol CO2 m-2 s-1)and carboxylation efficiency (0.042 to 0.275 mol m-2 s-1 [mol * mol-1]-1) were found from the asymptotic responses of net photosynthesis as a function of carbon dioxide concentration (0 to 750 mol mol-1). The greatest rates of net photosynthesis at ambient carbon dioxide concentration and optimum irradiance were found among the species in the following order: P. virginica ≥ T. distichum ≥ O. aquacticum > J. effusus. The divergent patterns of net photosynthesis as a function of irradiance and carbon dioxide concentration among the four species are important in understanding each species' intrinsic capacity to assimilate carbon in the wetland environment. These patterns also maintain distinct differences from the exhibited net photosynthetic patterns of species grown in upland agroecosystems (i.e., Zea mays var. rugosa, & Glycine max soja) at ambient carbon dioxide concentration and full light.
Key words: aquatic macrophytes, net photosynthetic rates
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